1. Field of the Invention
This invention relates to an indicating device for use in a camera for indicating, by the driving current from an electronic flash device, that the main capacitor of the electronic flash device has been charged to a predetermined value, that is, the electronic flash device is ready to emit flashlight.
2. Description of the Prior Art
The indicating device of this type employs a light-emitting element such as LED as an indicating element and this leads to a disadvantage that if the power source voltage of the electronic flash device fluctuates, the luminance of the light-emitting element is varied and the indication thereby becomes less easy to visually perceive. To eliminate such disadvantage, a constant current circuit may be series-connected to the light-emitting element and the constant current thereof may be used as the current for turning on the light-emitting element. Such constant current circuit may be provided within either the electronic flash device or the camera. However, if it is provided within the electronic flash device, there will occur a difficulty. That is, a camera permits various electronic flash devices to be mounted thereto and therefore, in order that the luminance of the light-emitting element within the camera may always be rendered substantially constant irrespective of the type of the electronic flash device mounted to the camera, the outputs of the constant current circuits of the various electronic flash devices must be equalized. This is difficult to achieve. Therefore, it is desirable that the constant current circuit be provided within the camera.
On the other hand, there is already known a tuned shutter time automatically setting circuit for automatically setting, for example, the shutter time of the electric shutter of the camera to the synchronizing time with which flash synchronizes, namely, the shutter time for which the shutter is fully open, in response to said driving current from the electronic flash device when mounted to a camera. Such synchronizing shutter time automatically setting circuit has generally been made into an integrated circuit.
Therefore, in a case where a camera is provided with such a synchronizing shutter time automatically setting circuit made into an integrated circuit and said constant current circuit series-connected to the light-emitting element, when the power source voltage of the electronic flash device is very great and the voltage across the series circuit comprising the constant current circuit and the light-emitting element is greater than the power source voltage of the camera, this great voltage is applied to the synchronizing shutter time automatically setting circuit made into an integrated circuit. This may lead to an undesirable possibility that the synchronizing shutter time automatically setting circuit malfunctions or is damaged.
Such malfunctioning or damage of the integrated circuit such as the synchronizing shutter time automatically setting circuit may occur not only in a case where the constant current circuit is connected to the aforementioned light-emitting element, but also in a case where provision is made of a current control circuit for controlling or limiting the current flowing to the light-emitting element for some purpose or other.